@ ScottA - Your lips don't have oil glands, (AKA, sebaceous glands)! The only oil layer on them is one you put there, (or you can use a wax). Interestingly, they also have no hair follicles & no melanin. Saliva is the only source of moisturization the body provides for lips & as SilverMinxxx said, it dries out quickly.

With one, now former GF, we were just fooling around, and I had not "really" intending on penetrating her. However, my pre-cum was sufficient for an easy entry, so we went with it. We did then use lube for more extended anal intercourse.

I’ve taken my husband in my ass three times with no lube whatsoever. It was very slow going but became a lot easier after tne minutes or so. To my great surprise, it didn’t really hurt and felt great. That being said, I’d still take lube anyday over dry. I’m not a patient woman when it comes to anal. - K